Futaba Sky Sport 5-Channel Upgrade

The Futaba Sky Sport Radio has been around for a number of years in various forms and versions.  I purchased one in 2005.  It always bugged me that opposite the trainer switch was a plastic plug that looked like there should be another switch.

One day out of curiosity, I took it apart and began to study the circuit board.  In most radios, there is a multiplexing chip that reads the state of the various inputs and converts it to a PPM serial stream that is fed to the RF unit.  The receiver then decodes this pulse train and uses it to signal the individual servos.  Following the wires from the joystick pots to where they attached to the board (shown in RED below), and then the traces on the board, I figured out which IC was the multiplexer. (shown in BLUE)  After some internet searching and following the other traces feeding into and out of the IC, I found three unused solder pads on the board. (shown in GREEN)  Two were 0V and +5V and the third went back to the multiplexer.  I thought, "It can't be that simple."  I soldered in a 5th pot and wired it to the spare solder pads.

To my surprise it was just that easy!  Why the radio was not built this way, I don't know.  It even came with a 7-channel receiver and I am not a aware of a factory 5 channel version that would have been built on the same framework.